The invention relates in general terms to the processing of data received in a chip card, also referred to as a microcomputer or microprocessor card (smart card).
The service providers managing chip cards have a greater and greater requirement to store a large number of data in the non-volatile memory of the EEPROM or Flash EEPROM type contained in the chip card. The memory capacity requirements of chip cards also have a tendency to increase because of the use of certain software packages written in programming languages, such as Java, for which parts of programs, such as applets, are to be downloaded into the cards.
In order to give an idea, if 5 kilobytes are transmitted in each of 1 million cards with a single terminal operating 24 hours a day and 7 days a week and whose output is 9600 bits/second, more than 2 months are needed to load these data into the cards.
In radiotelephony, the chip card is integrated as an SIM (Subscriber Identity Module) in the portable radiotelephone terminals. The active state of the radiotelephone terminal and therefore its current consumption and its battery life depend notably on the time taken to transmit the data to be processed by the SIM card.
In more general terms, the reduction in the time taken for transmission of the data to be downloaded into the chip cards is an indisputable gain vis-à-vis both the terminal loading the data into the chip card and vis-à-vis the card itself and the transmission support(s) or channel(s) conveying the data to be downloaded.
In addition the Japanese patent application 08235329 filed on 24 Feb. 1995 proposes downloading compressed data into a memory card, that is to say a “static” card which does not process the data which it receives and serves as a remote memory with respect to an image processing unit which produced the compressed data. The image processing unit writes to two first predetermined addresses in the memory card respectively the length of the data before compression and the length of the data after compression, and then writes the compressed data in the memory card. Conversely, when the compressed data are loaded from the memory card into the image processing unit, the image processing unit reads the length of the data before compression and the length of the data after compression at the respective two aforementioned addresses, and then reads the compressed data so as to decompress them in accordance with a predetermined decompression algorithm installed in the image processing unit.